Sign started work on January 22, 1948 and would go on to last 386 intensive days. Indeed, so intensive and thorough was Sign in its investigation that the public was given the impression that the project was a top military priority. This contrasted sharply with the public reports coming out of Sign, which consisted of terse, uninformative explanations for UFO phenomena. The combination of intense work and pithy reports almost immediately bred whispers of a cover-up. These whispers grew to a dull roar as the results of Sign's first major investigation (into the death of Captain Thomas F. Mantell, Jr., who died while pursuing a UFO) were released to the public. Dr. J. Allen Hynek's written report on the investigation could be summed up as "Venus and other stuff. Case closed." The public didn't like that very much.

In reality, the turmoil within the project was due to something much more down-to-earth than an interplanetary conspiracy — namely, disagreements and infighting. Proponents of the ETH (extraterrestrial hypothesis) within Sign were pressuring other investigators to label cases 'Unknown' unless proof was absolute. On the other hand, other investigators felt than an unproven, prosaic exclamation was preferable, considering the alternative was allowing the public to fantasize and panic about little green men.

The internal fuss over the Mantell case was a sign that the ETH contingency was growing in number and stature within the team, and, after a few additional 'Unknown' cases, they were the clear majority. A case involving the sighting of a cigar-shaped spacecraft outside of a DC-3 was the last nail in the coffin for the skeptics. One investigator wrote "that this development is possibly of foreign origin would seem to be a logical premise." "Foreign" was not referring to the Russians. A majority of the team agreed.

In September 1948, Sign issued their final report, Estimate of the Situation, to the Air Force's top brass. It examined several of the 'Unknown' cases, many with reliable witnesses and documentation. The conclusion of this TOP SECRET report to the highest levels of the USAF?

USAF Chief of Staff General Hoyt S. Vandenburg received the report in October. He immediately stated that Project Sign's conclusions were not supported by their evidence. All copies of Estimate of the Situation were to be burned. ETH proponents were slowly reassigned away from Project Sign until the skeptics were once again in the majority. Project Sign officially died on February 11, 1949, when it was reborn as Project Grudge.

The Air Force would deny the existence and the burning of Estimate of the Situation for years, even after declassifying the whole of Project Sign. To even the most casual and patriotic of observers, it was obvious that the Air Force was lying. The government's refusal to come clean would come back to haunt them, for Estimate of the Situation would soon become the "smoking gun" of UFO cover-up theorists.

But Sign was not part of a cover-up. The secrecy surrounding the Project in its final days was nothing more than a giant cluster fuck, a huge public relations mistake that the government would soon regret. The easiest way to earn the public's mistrust is to keep secrets when you have nothing worth hiding. Sign is the story of how not to run a military-sponsored UFO investigation team.